Positron Emission Tomography (PET) is an in vivo analog of autoradiography and has the potential to become a powerful new tool in imaging biological processes in small laboratory animals. With the ever increasing number of human disease models, particularly in the smaller animals such as mice and rats, high resolution radionuclide imaging (such as PET) of small animals can contribute unique information. The critical advantage of PET is that it allows functional information to be obtained non-invasively, so each animal can be studied repeatedly. Clinical PET scanners used for human imaging are bulky, expensive and do not have adequate spatial resolution for small animal studies. Hence, dedicated, low cost instruments are required for conducting small animal studies with higher spatial resolution than what is currently achieved with clinical PET scanners. The goal of the proposed effort is to investigate a novel approach for designing a high resolution PET system. PROPOSED COMMERCIAL APPLICATION: Radionuclide imaging (PET, SPECT, gamma-camera, surgical probes), high energy physics, nuclear and health physics, nuclear treaty verification, nuclear safeguards.